1869.] Fhysies. 149 



tion of brightness. These hands could not be resolved into lines, 

 nor was any light seen beyond the bands towards the violet and 

 the red. 



The author found this cometic spectrum to agree exactly with a 

 form of the spectrum of carbon which he had observed and measured 

 in 1864. When an induction spark, with Leyden jars intercalated, 

 is taken in a current of olefiant gas, the highly heated vapour of 

 carbon exhibits a spectrum which is somewhat modified from that 

 which may be regarded as typical of carbon. The light is of the 

 same refrangibilities, but the sej^arate strong hnes are not to be 

 distinguished. The shading, comjwsed of numerous fine lines, 

 which accompanies the lines appears as an unresolved nebulous 

 light. 



On comparing the spectrum of the comet directly in the spec- 

 troscope with the S25ectrum of the induction spark taken in a current 

 of olefiant gas, the three bands of the comet apj)eared to coincide 

 with the corresponding bands of the spectrum of carbon. In 

 addition to an apparent identity of position, the bands in the two 

 spectra were very similar in their general characters and in their 

 relative brightness. The remarkably close resemblance of the spec- 

 trum of the comet to that of the spectrum of carbon necessarily 

 suggests the identity of the substances by which in both cases the 

 light was emitted. 



Heat. — The intense heat of the voltaic arc has been applied 

 by F. P. Le Koux in a most ingenious manner to heighten the 

 brilliancy of the light, and at the same time to increase its. steadi- 

 ness. In applying electric light, the method generally proposed is 

 to direct it into a more or less limited region of space ; all which 

 escapes into the opposite region would be lost if it were not. col- 

 lected by reflectors more or less appropriate to the pm-pose. On 

 the other hand, experience has proved that the voltaic arc is prone 

 to irregular displacements, consequent upon inequalities in the co- 

 hesion of the charcoal, impurities contained in it, and above all, the 

 slightest agitation of the air. The most luminous portions of the 

 charcoal electrodes being the siu^faces between which the are arises,, 

 these sm-faces are inclined sometimes in one direction and sometimes 

 in another, by reason of the displacement which the arc undergoes, 

 the result being a considerable variation in the effect of light pro- 

 duced by the latter in any determinate region. M. Le Eoux argued, 

 in the course of his investigation, that if there could be placed on 

 the opposite side to that towards which the light was to be directed, 

 and in proximity to the arc, some body capable of reflecting back 

 in a luminous form the enormous number of radiations thrown 

 upon it by the electrodes and the arc itself, these radiations would 

 be more profitably utilized than by any other method, the arc being 



